The amphibious airplane offers unparalleled utility. It also provides for a greater measure of safety than the conventional land airplane. The amphibious airplane is designed to operate from rough airports and available waterways, with or without prepared surface, docking or handling facilities. It is also well suited for operation in remote and undeveloped areas as well as operation in the downtown area of major cities, most of which have sufficient water available for a suitably designed amphibious airplane. After landing on water, the amphibious airplane can taxi onto the adjacent land for boarding and unloading passengers and servicing in the manner of a conventional airplane.
While in transit, every river, pond or lake over a half mile long having reasonably calm water with waves of about two feet or less is an emergency landing field, as are the usual fields and smaller airports. Furthermore, the hull bottom of amphibious airplanes, which are generally stronger than the bottom of the conventional airplane fuselage because of the design requirements of water landing loads, offers more protection in the event of a forced landing.
Despite these enormous advantages, the amphibious airplane does not enjoy any measure of utilization today. Higher initial costs, higher operating costs and generally poorer performance in terms of speed, payload and range have made them unattractive relative to conventional airplanes. This situation exists because of several persistent problems related to the design of amphibious airplanes.
One problem is greater weight because of increased hull structural strength required to absorb the high loads of water landings, which increase substantially with the higher landing speeds generally associated with high performance airplanes. The wings of high performance airplanes are usually designed for the high speed, high altitude flight regime requirements rather than the low speed take-off landing requirements and therefore the high performance airplanes have high stalling speeds and thus high landing speeds. This increased structural weight requires greater engine power, which, in turn, increases the weight still further with the result of both larger initial costs and operating expense. Furthermore, increases in weight and aerodynamic drag result from the traditional V-shape hulls required to absorb the high landing loads, the transverse step required for water take-off, the wing tip floats usually required for transverse stability in the water or the poorly designed hull tunnel of those airplanes using sponsons for transverse stability instead of floats, and the landing gear either hanging in the airstream or stowed in an unsatisfactory manner.
The result of these unsatisfactory designs is substantial degradation of air speed, range and payload and high fuel consumption.
Another problem plaguing the amphibious airplane has been higher maintenance costs associated with water spray, especially the ingestion of water by engines. Added maintenance also results from the water penetrating the air frame through the lower portions of the fuselage and hull due to breach of integrity of these surfaces which traditionally housed retractable landing gear. This problem increases in severity with the increasing landing speeds of high performance aircraft. In the past, engineering design changes have not solved or even substantially alleviated these problems.
The successful amphibious executive airplane must be able to take-off from and land on short airfields or inland water with waves of approximately two feet or less, at low speeds (about 70 to 80 knots). It also must accelerate smoothly to high altitudes (about 35,000 to 40,000 feet) and cruise efficiently at high speeds (Mach number about 0.8) or better for significant distances (about 1,500 to 2,000 miles) carrying at least 6 to 8 passengers and crew. This requires high lift on take-off and landing and thus high aspect ratio wings with large area and the exact opposite during cruise, that is, lower aspect ratio wings with decreased surface area. Further requirements for such a low drag, aerodynamically efficient airplane dictate that the landing gear must retract and be stowed within the airplane. There can be no wing floats or hull steps, and fuselage mounted sponsons for landing and take-off and lateral transverse stability in the water, as well as the hull itself, must be aerodynamically and hydrodynamically clean and efficient. Water spray and especially ingestion by the engines must be eliminated or kept to an absolute minimum. In addition, the requirement for integrity of the hydrodynamic planing surfaces would preclude the use of hydrofoils or hydroskis, which are otherwise not desirable because of their added weight and operational complexity.